1. Field of the Invention
The present invention is an implantable surgical device system and method for delivering therapeutic levels of energy to tissue in a living body. More specifically, it is a long-term implantable system and method for delivering therapeutic levels of ultrasound energy invasively within the body in order to treat chronic disorders associated with skeletal joints. Still more specifically, it is a long-term implant system and method for delivering therapeutic ultrasound energy to spinal joints, such as in particular intervertebral discs or associated bony vertebral structures.
2. Description of the Background Art
For many years, much research and commercial development has been directed toward delivering energy to tissue in order to achieve various desired therapeutic results. Examples of energy modalities previously described for tissue treatment include: electrical current (both DC and AC, e.g. radiofrequency or “RF” current), plasma ion energy, sonic energy (in particular ultrasound), light energy (e.g. laser, infrared or “IR”, or ultraviolet or “UV”), microwave induction, and thermal energy (e.g. convection or conduction). Other modalities for treating tissue include without limitation: cryotherapy (cooling tissue to desired levels to affect structure of function), and chemical therapy (delivering chemicals to the tissue to affect the tissue structure of function). Each of these energy delivery and other treatment modalities has been extensively studied and characterized as providing unique benefits, as well as unique issues and concerns, with respect to tissue therapy. Accordingly, many specific energy delivery methods and systems have been disclosed to provide unique benefits for particular intended therapeutic applications.
Various specific tissue responses to energy delivery have also been observed and reported during the course of significant study and characterization. In one regard, tissues or their function may be damaged by energy delivery such as thermal therapy. Examples of previously disclosed, differentiated effects of thermal tissue therapy generally characterized to damage tissue include, without limitation: ablation (which has been defined as either molecular dissociation or by achieving cellular necrosis), coagulation, degranulation, and desiccation. Alternatively, energy delivery in certain particular forms has also been characterized as promoting reproductive stimulation in certain tissues. Certain desired results have been disclosed with respect to intending controlled tissue damage with tissue thermal therapy; other desired results have been disclosed with respect to promoting tissue reproduction with tissue thermal therapy. In any event, because of the pronounced effects observed from tissue energy delivery, it is often desired to control and accurately select the localization of tissue/energy interaction in order to treat only the intended tissue, else normal surrounding tissue is effected with harmful results.
Accordingly, the different energy delivery modalities have been specifically characterized as providing particular benefits and problems versus other modalities with respect to various specific tissues and related medical conditions. Examples of specific medical conditions and related tissue that have been studied and characterized for tissue energy delivery include: tumors such as cancer (e.g. liver, prostate, etc.); vascular aneurysms, malformations, occlusions, and shunts; cardiac arrhythmias; eye disorders; epidermal scarring; wrinkling; and musculo-skeletal injury repair. The nature of the condition to be treated, as well as the anatomy of the area, can have significant impact on the desired result of energy delivery, which directly differentiates between the appropriateness or inappropriateness of each of the different energy delivery modalities for such application (as well as the corresponding particular operating parameters, systems, and methods for delivering such energy).
Depending upon the particular energy modality, various different parameters may be altered to affect the thermal effect in particular tissues, including which type of effect is achieved (e.g. ablation, coagulation, desiccation, etc.), as well as depth or degree of the effect in surrounding tissues. For the purpose of a general understanding, however, known tissue responses to thermal therapies, e.g. effect of changing temperatures to particular levels, have been previously characterized for certain tissues in prior disclosures which are summarized as follows.
As described above, temperature elevation of biological tissues is currently used for outright tissue destruction or to modify tissues to enhance other therapies. Low temperature elevations (41-45° C.) of relatively short duration (<30-60 min) have been disclosed as being associated with cell damage, but generally only to such extent to be repairable and considered non-lethal. In this range, it is believed that heat mediated physiological effects include heat induced acceleration of metabolism or cellular activity, thermal inactivation of enzymes, rupture of cell membranes, and delayed onset of increasing blood flow and vessel permeability. Prior disclosures addressing temperature exposures in excess of 45° C. and/or longer durations have stated that cellular repair mechanisms no longer function due to denaturation of key proteins or can't keep up with the accumulating damage. According to thermal therapy at such temperatures, complete cell death and necrosis have been observed in certain particular tissues to be fully expressed in approximately 3-5 days. Temperature exposures in the 42-45° C. regimen are commonly used for example as an adjuvant to radiation cancer therapy and chemotherapy, and have been considered for enhancing gene therapy and immunotherapy as well. Higher temperature elevations (50+° C.) have been investigated for inducing desirable physical changes in tissue, ranging from applications such as controlled thermal coagulation for “tightening” ligaments and joint capsules, tissue reshaping, and selective tissue thermal coagulation for destroying cancerous and benign tumors. High temperature exposures (50+° C.) are generally believed to produce rather lethal and immediate irreversible denaturation and conformational changes in cellular and structural proteins in various tissues, thereby thermally coagulating such tissues.
In general, heat-induced cell damage or tissue structural changes described above are believed to be attributed to thermal denaturation and aggregation of key protein structures. The accumulation of this thermal damage can be modeled using the Arrhenius rate process equation, which establishes a relationship between rate of thermal damage and the duration and temperature of exposure:
                                          1            τ                    =                      A            ·                          ⅇ                                                -                  Δ                                ⁢                                                                  ⁢                                  E                  /                  RT                                                                    ,                            (        1        )            where ΔE is activation energy (J mol−1), R is the universal gas constant (8.32 J mol−1K−1), A is the rate constant (s−1), T is temperature in Kelvin, and 1/τ is rate of thermal damage (s−1). Using this expression (Eqn. 1), a relationship can be derived to determine an exposure time (τ2) and/or temperature elevation (T2) required to produce an equivalent observed biological effect associated with a specified temperature (T1) and time exposure (τ1). This is the basis of the thermal iso-effect equation as shown below, which is non-linear with respect to temperature exposure and linear with respect to exposure time:τ2=τ1e(ΔE/RT1T2)(T1−T2)=τ1K(T1−T2),  (2)where the parameter K is approximated as constant for typical therapeutic temperature elevations (10-30° C.). Furthermore, extensive in vitro and in vivo studies have demonstrated that ΔE for thermal damage is approximately constant at 140 J mol−1 for temperatures greater than 43° C. Thus, the relationship between time and temperature for a given biological effect depends upon activation energy only. Thus, as determined from the hyperthermia biology literature, K≅2 for T≧43° C. and K≅4-6 for T<43° C. The different values split at approximately 43° C. in order to model the biphasic behavior in the rate response, with faster damage accumulation after a break around 43° C. These values hold for lethal cellular damage, but not coagulation of structural proteins (collagen). Traditionally this iso-effect dose has been used to characterize hyperthermia cancer treatments with a target temperature elevation of 42.5-45° C., and has led to 43° C. becoming the historical reference dose temperature. This forms the basis of the thermal iso-effect dose (TID) equation, which as shown below can be used to calculate thermal dose of a varying temperature exposure over time as an equivalent exposure duration at 43° C. (or other reference temperature). Temperature time history is equated to a thermal dose at a known temperature reference.
                                          EM            43                    =                                                    ∫                0                                  t                  f                                            ⁢                                                K                                      (                                          T                      -                      43                                        )                                                  ⁢                                  ⅆ                  t                                                      =                                          ∑                                  t                  =                  0                                                  t                  final                                            ⁢                              Δ                ⁢                                                                  ⁢                                  tK                                      (                                          T                      -                      43                                        )                                                                                      ,                            (        3        )            where dt is a time step (min) and EM43 is thermal dose expressed in equivalent minutes at 43° C.
Various previously published disclosures have verified the Arrhenius model and the iso-effect relationship of different temperature-time exposures for generating trans-epidermal thermal necrosis in skin. Applying the TID analysis, a threshold of approximately 320 EM43 (wherein “EM” represents “equivalent minutes” at the given temperature shown in subscript) as found for temperatures between 44-60° C. Thermal dosages between 10-100 EM43 have been shown to correlate with improved response to hyperthermia and radiation therapy. For a conservative approach 250 EM43° C. is a threshold dose for complete thermal necrosis, where reported values range from 25-240 EM43° C. for brain and muscle tissue, respectively.
In addition, thermal coagulation or coagulation necrosis have been disclosed to occur in tissues exposed to temperatures greater than approximately 55° C. for a duration of minutes, in particular respect to collagen in certain structures studied. Thermal coagulation of soft tissues generally takes place only for temperatures in excess of 50° C. Numerous investigators have validated the “TID” (or “temperature iso-dose”) concept for predicting lesions using 240-340 EM 43° C. as a threshold dose and critical temperatures of 53-54° C. for coagulating muscle.
Therapeutic Energy Delivery for Spinal Disorders
Spinal disorders have been the topic of significant study and commercial development for therapeutic energy delivery. In particular, various specific conditions that have been studied with respect to particular modes of therapeutic energy delivery.
Of particular interest has been chronic lower back pain. Chronic low back pain is a significant health and economic problem in the United States, being the most costly form of disability in the industrial setting. For a substantial number of these patients the intervertebral disc is considered the principal pain generator. Traditionally, patients who fail conservative therapy have few treatment options beside discectomy or fusion, either of which can result in significant morbidity and variable outcomes. Recent efforts have been directed toward investigating thermal therapy for providing a healing effect on collagenous tissues, and therefore this modality has been incorporated into several minimally invasive back pain treatments.
Early orthopedic use of high temperature heat therapy was to manage shoulder instability. In this application, the shoulder capsule is treated with laser or radio-frequency (RF) thermal energy to temperatures typically in the range of 70 to 80° C. This treatment has been disclosed to stabilize the joint by inducing tissue contraction. Such treatment also has been disclosed to result in an acute decrease in stiffness (e.g. as much as 50%) that may be recovered due to biologic remodeling. However, the long-term benefits of this treatment have been questioned since the collagenous tissue may re-lengthen over time.
The contraction associated with thermal therapy, which can reach as high as 50% along the fiber direction in the shoulder capsule, has been correlated with thermal denaturation. Thermal denaturation is an endothermic process in which the collagen triple helix unwinds after a critical activation energy is reached. Differential scanning calorimetry (DSC) is a technique to measure both the denaturation temperature (Tm—the peak temperature corresponding to this critical activation energy) and the total enthalpy of denaturation (ΔH—the total energy required to fully denature the collagen). This technique can be used to correlate thermal exposure with the resulting degree of denaturation for a specific collagenous tissue, and thus to guide the development of an optimal thermal dose.
Intradiscal electrothermal therapy (IDET) has been recently introduced as a minimally invasive, non-operative therapy in which a temperature elevation is applied in order to treat discogenic low back pain. In this procedure, a temporary catheter containing a 5 cm long resistive-wire heating coil is introduced percutaneously into the disc under fluoroscopic guidance. The internal temperature of the device is then raised from 65° C. to 90° C. over a course of 16 minutes. This procedure is intended to produce temperatures sufficient to contract annular collagen and ablate annular nociceptors. A controlled, 12 month trial of IDET on a relatively small patient population (36 individuals) demonstrated some relief of back pain in 60% of patients and total relief in 23%. A two-year follow-up study of 58 patients was disclosed to result in clinically significant improvement in pain, physical function, and quality of life. While these results have been considered by some to be promising, prospective placebo-controlled trials are lacking, and the therapeutic mechanisms of thermal therapy are unknown. Proposed therapeutic mechanisms of such technique have included: 1) collagen denaturation, causing annular stiffening, and tissue remodeling; 2) annular de-innervation; and 3) ablation of cytokine-producing cells. Due to mechanistic uncertainty, treatment optimization and patient selection are generally empirically based.
The effect of heat on collagen denaturation and biomechanical properties has been investigated in various tissues: knee and shoulder capsule, tendon, and chordae tendineae. In general, at least one prior disclosure reports that significant denaturation and shrinkage occurred in tissue treated at 65° C. and above for 1-5 minutes. However, given that the annular architecture of intervertebral discs is quite different from these other tissues it is has not been previously made clear that prior results can be directly extrapolated to the intervertebral disc.
Further more detailed background information related to various aspects of thermal tissue therapy and/or chronic back pain is variously disclosed in the following publications: Amonoo-Kuofi, H. S., 1991, “Morphometric changes in the heights and anteroposterior diameters of the lumbar intervertebral discs with age.” J Anat 159-68;
Arnoczky, S. P. and Aksan, A., 2001, “Thermal modification of connective tissues: basic science considerations and clinical implications.” Instr Course Lect 3-11; Chen, S. S., Wright, N. T. and Humphrey, J. D., 1997, “Heat-induced changes in the mechanics of a collagenous tissue: isothermal free shrinkage.” J Biomech Eng 4, 372-8; Chen, S. S., Wright, N. T. and Humphrey, J. D., 1998, “Heat-induced changes in the mechanics of a collagenous tissue: isothermal, isotonic shrinkage.” J Biomech Eng 3, 382-8; Dewey, W. C., 1994, “Arrhenius relationships from the molecule and cell to the clinic.” Int J Hyperthermia 4, 457-83; Flandin, F., Buffevant, C. and Herbage, D., 1984, “A differential scanning calorimetry analysis of the age-related changes in the thermal stability of rat skin collagen.” Biochim Biophys Acta 2, 205-11; Gerber, A. and Warner, J. J., 2002, “Thermal capsulorrhaphy to treat shoulder instability.” Clin Orthop 400, 105-16; Hall, B. K., 1986, “The role of movement and tissue interactions in the development and growth of bone and secondary cartilage in the clavicle of the embryonic chick.” J Embryol Exp Morphol 133-52; Hayashi, K. and Markel, M. D., 2001, “Thermal capsulorrhaphy treatment of shoulder instability: basic science.” Clin Orthop 390, 59-72; Hayashi, K., et al., 2000, “The mechanism of joint capsule thermal modification in an in-vitro sheep model.” Clin Orthop 370, 236-49; Hayashi, K., et al., 1997, “The effect of thermal heating on the length and histologic properties of the glenohumeral joint capsule.” Am J Sports Med 1, 107-12; Heary, R. F., 2001, “Intradiscal electrothermal annuloplasty: the IDET procedure.” J Spinal Disord 4, 353-60; Hecht, P., et al., 1999, “Monopolar radiofrequency energy effects on joint capsular tissue: potential treatment for joint instability. An in vivo mechanical, morphological, and biochemical study using an ovine model.” Am J Sports Med 6, 761-71; Karasek, M. and Bogduk, N., 2000, “Twelve-month follow-up of a controlled trial of intradiscal thermal anuloplasty for back pain due to internal disc disruption.” Spine 20, 2601-7; Kronick, P., et al., 1988, “The locations of collagens with different thermal stabilities in fibrils of bovine reticular dermis.” Connect Tissue Res 2, 123-34; Le Lous, M., et al. 1982. “Influence of collagen denaturation on the chemorheological properties of skin, assessed by differential scanning calorimetry and hydrothermal isometric tension measurement.” Biochim Biophys Acta 2, 295-300; Lopez, M. J., et al., 2000, “Effects of monopolar radiofrequency energy on ovine joint capsular mechanical properties.” Clin Orthop 374, 286-97; Miles, C. A. and Ghelashvili, M. 1999, “Polymer-in-a-box mechanism for the thermal stabilization of collagen molecules in fibers.” Biophys J 6, 3243-52; Naseef, G. S., et al., 1997, “The thermal properties of bovine joint capsule. The basic science of laser- and radiofrequency-induced capsular shrinkage.” Am J Sports Med 5, 670-4; Nieminen, M. T., et al., 2000, “Quantitative MR microscopy of enzymatically degraded articular cartilage.” Magn Reson Med 5, 676-81; (Nrc/lm), N. R. C. A. I. O. M. (2001). “Musculoskeletal Disorders and the workplace: low back and upper extremities.” Washington D.C., National Academy Press; Saal, J. A. and Saal, J. S., 2002, “Intradiscal electrothermal treatment for chronic discogenic low back pain: prospective outcome study with a minimum 2-year follow-up.” Spine 9, 966-73; discussion 973-4; Saal, J. S. and Saal, J. A., 2000, “Management of chronic discogenic low back pain with a thermal intradiscal catheter. A preliminary report.” Spine 3, 382-8; Schachar, R. A., 1991, “Radial thermokeratoplasty. Int Ophthalmol” Clin 1, 47-57; Schaefer, S. L., et al., 1997, “Tissue shrinkage with the holmium:yttrium aluminum garnet laser. A postoperative assessment of tissue length, stiffness, and structure.” Am J Sports Med 6, 841-8; Schwarzer, A. C., et al., 1995, “The prevalence and clinical features of internal disc disruption in patients with chronic low back pain.” Spine 17, 1878-83; Urban, J. P. and Mcmullin, J. F., 1985, “Swelling pressure of the intervertebral disc: influence of proteoglycan and collagen contents.” Biorheology 2, 145-57; Vangsness, C. T., Jr., et al., 1997, “Collagen shortening. An experimental approach with heat.” Clin Orthop 337, 267-71; Vujaskovic, Z., et al., 1994, “Effects of intraoperative hyperthermia on peripheral nerves: neurological and electrophysiological studies.” Int J Hyperthermia 1, 41-9; Wallace, A. L., et al., 2000, “The scientific basis of thermal capsular shrinkage.” J Shoulder Elbow Surg 4, 354-60; and Wallace, A. L., et al., 2002, “Creep behavior of a rabbit model of ligament laxity after electrothermal shrinkage in vivo. Am J Sports Med 1, 98-102. The disclosures of these references are herein incorporated in their entirety by reference thereto.
Chronic lower back pain (e.g. discogenic lumbar pain) and related motor nerve deficit is typically due to damaged or herniated vertebral discs which either directly impinge on surrounding nerves or cause irritating inflammation. Traditional treatment options include surgery, anti-inflammatory drugs, physical therapy, etc., with surgery typically the last option. Due to difficulty of surgical procedure, complications and time of recovery, alternative procedures have been investigated. Recently, intradiscal thermal therapy has been introduced as a minimally-invasive alternative in the treatment of various spinal disorders such as chronic low back pain and otherwise disorders related to intervertebral disc abnormalities.
In particular, several different systems and methods have been disclosed for treating various abnormal conditions associated with intervertebral discs specifically by delivering electrical current in the RF range during invasive treatment procedures in and around the disc within the body. Other previously disclosed examples intended to invasively deliver therapeutic levels of energy in order to treat various spinal disorders include delivery of plasma ion energy (e.g. CoblationR from Arthrocare, Inc.), laser light energy, or thermal energy from conductive heating elements (e.g. the SpineCATH DEC procedure, commercially available from Oratec Interventions, introduced above). At least one other prior disclosure is intended to deliver heated thermoplastic material to allow it to flow into and then set upon cooling within the nucleus of an intervertebral disc in order to replace the nucleus pulposus.
Further more detailed examples of energy delivery systems and methods such as of the types just described, that are intended to provide invasive therapy to treat various conditions associated with intervertebral disc disorders are variously disclosed in the following issued U.S. Pat. Nos. 4,959,063 to Kojima; 6,264,650 to Hovda et al.; 6,264,659 to Ross et al. Examples are also disclosed in the following published U.S. Patent Application: US 2001/0029370 to Hodva et al., now U.S. Pat. No. 6,464,695. Other examples are disclosed in the following published international patent applications: WO 00/49978 to Guagliano et al.; WO 00/71043 to Hovda et al.; WO 01/26570 to Alleyne et al. Additional disclosure is provided in the following published reference: Diederich C J, Nau W H, Kleinstueck F, Lotz J, Bradford D (2001) “IDTT Therapy in Cadaveric Lumbar Spine: Temperature and thermal dose distributions, Thermal Treatment of Tissue: Energy Delivery and Assessment,” Thomas P. Ryan, Editor, Proceedings of SPIE Vol. 4247:104-108. The disclosures of all these references provided in this paragraph are herein incorporated in their entirety by reference thereto.
Ultrasound energy delivery and the effects of such energy on various different tissue structures has been the topic of significant recent study. The particular benefits of ultrasound delivery have been substantially well characterized, in particular with respect to different types of tissues as well as different ultrasound energy deposition modes. Many different medical device systems and methods have been disclosed for delivering therapeutic levels of ultrasound to tissues to treat wide varieties of disorders, including for example arterial blockages, cardiac arrhythmias, and cancerous tumors. Such disclosures generally intend to “ablate” targeted tissues in order to achieve a desired result associated with such particular conditions, wherein the desired response in the particular tissues, and the ultrasound delivery systems and methods of operation necessary for the corresponding energy deposition modalities, may vary substantially between specific such “ultrasound ablation” systems and methods.
Further more detailed examples of ultrasound delivery systems and methods such as of the type just described are disclosed in the following issued U.S. patents which are incorporated herein by reference: U.S. Pat. Nos. 5,295,484 to Marcus et al.; 5,620,479 to Diederich; 5,630,837 to Crowley; 5,733,280 to Sherman et al.; 6,012,457 to Lesh; 6,024,740 to Lesh et al.; 6,117,101 to Diederich et al.; 6,164,283 to Lesh; 6,245,064 to Lesh et al.; 6,254,599 to Lesh et al.; and 6,305,378 to Lesh et al. Other examples are disclosed in the following published foreign patent applications which are incorporated herein by reference: WO 00/56237 to Maguire et al.; WO 00/67648 to Maguire et al.; WO 00/67656 to Maguire et al.; WO 99/44519 to Langberg et al.
In addition, ultrasound enhanced drug delivery into tissues, e.g. to increase dispersion, permeability, or cellular uptake of therapeutic compounds such as drugs, has been well characterized and disclosed in many different specific forms.
Further more detailed examples of ultrasound energy delivery systems and methods such as those just described are disclosed in the following U.S. Pat. Nos. 5,725,494 to Brisken; 5,728,062 to Brisken; 5,735,811 to Brisken; 5,846,218 to Brisken et al.; 5,931,805 to Brisken; 5,997,497 to Nita et al.; 6,210,393 to Brisken; 6,221,038 to Brisken; 6,228,046 to Brisken; 6,287,272 to Brisken et al.; and 6,296,619 to Brisken et al. The disclosures of these references are herein incorporated in their entirety by reference thereto.
Additional previously disclosed examples for ultrasound energy delivery systems and methods are intended to treat disorders associated with the spine in general, and in some regards of the intervertebral disc in particular. However, these disclosed systems are generally adapted to treat such disorders chronically from outside of the body, such as for example via transducers coupled to a brace worn externally by a patient. Therefore locally densified US energy is not achieved selectively within the tissues associated with such disorders invasively within the body. At least one further disclosure, however, proposes delivering focused ultrasound energy from outside the body for the intended purpose of treating intervertebral disc disorders, in particular with respect to degenerating the nucleus pulposus to reduce the pressure within the disc and thus onto the adjacent spinal cord. However, the ability to actually achieve such targeted energy delivery at highly localized tissue regions associated with such discs, and to accurately control tissue temperature to achieve desired results, without substantially affecting surrounding tissues has not been yet confirmed or taught.
Further more detailed examples of such systems and methods intended to treat spinal disorders with ultrasound energy from outside of the body are variously disclosed in the following issued U.S. Pat. Nos. 5,762,616 to Talish; 6,254,553 to Lidgren et al. Other examples are disclosed in the following published international patent applications: WO 97/33649 to Talish; WO 99/19025 to Urgovich et al.; and WO 99/48621 to Cornejo et al. The disclosures of these references are herein incorporated in their entirety by reference thereto.
Exposure of soft and hard tissue, including the spine and joints, to varied degrees of heat or other energy delivery can provide varied therapeutic effects. For example, heat at high temperatures and thermal doses can shrink tissues, change the structural matrix, and generate physiological changes and/or kill cells. Heat at low temperatures and can generate permeability changes or changes in the cellular transport/metabolism that increase effectiveness or deposition of certain pharmaceutical agents.
Heat can be provided using ultrasound (US), radio frequency (RF), laser, and the like, using invasive or non-invasive application techniques. For example, in order to treat internally embedded sensitized nerves or cells making inflammatory factors, invasive techniques are preferred so that the heat source can be placed in close proximity to the target tissue. This can be accomplished using conventional surgical techniques, where the patient is opened, and a heat source is inserted directly (e.g., using a directly implantable device such as described in U.S. Pat. No. 5,620,497, incorporated herein by reference), or indirectly through a catheter or other delivery device. When the procedure is complete, the heat source is removed and the patient is closed.
However, despite the many benefits of temporary devices and their acutely delivered treatments, a single treatment or a contemporaneous series of discrete treatments in those previous examples may not provide adequate results in many cases. In one regard, the ability to treat many chronic ailments is limited in the setting of an acute invasion into the body required by temporary devices. Therefore, it may be necessary to repeat the treatment at a later date if a single application is not sufficient for the ailment. Accordingly, longer term implantable devices and treatments are preferred for many medical therapies.
In this regard, the term “temporary” as herein used to describe certain medical devices, systems, or methods, including with respect to implants, is intended to mean adapted for acute use, such as in a hospital or outpatient surgical room or suite, over a relatively short period of time. In general, patients do not carry temporary devices implanted within them away from a healthcare facility—they are used in an acute setting typically accompanied by observation by healthcare personnel (e.g. such observation by a healthcare provided may be either continuous, or for longer temporary treatments may be sporadic, or may simply initiate a procedure via an implant and return to remove it after a time specified or an endpoint parameter is met). The time period by which temporary medical devices are typically left indwelling within the body is usually on the order of minutes, or possibly hours, though in some extreme cases some temporary medical devices can be left indwelling for as much as 1-5 days (though again typically under professional care, such as during a hospital stay). Temporary medical devices also often include portions of the device extending externally of the patient's body, such as for example catheters or leads that interface with other cooperating hardware such as actuators or diagnostic systems.
In contrast, the terms “permanent implant” are herein intended to mean a medical device implant that is intended for long-term implantation for chronic therapy or use. In such cases, patient's carry such implant indwelling within their bodies during their daily lives. Typically, these permanent implants are intended for indefinite periods and associated with chronic conditions ameliorated or diminished by the permanent implant, but typically not cured upon removal of the permanent implant. As such, they are not generally intended to be removed, though often may require removal, such as for replacement due to limitation of the lifespan of the implant itself, or for example changing condition of the patient. Such changing conditions may include, for example and without limitation: growth with respect to pediatric patients, other changes in physique, changes in condition being treated or otherwise with respect to the environment and/or needs underlying the implant's presence.)
The terms “semi-permanent implant” are herein intended to mean implants that are intended for implantation over a period that lasts longer than considered under an “acute” setting, e.g. longer than typically provided for under the care of a healthcare provider and longer than most “temporary” medical devices such as temporary implants, though usually over a shorter period than most “permanent implants”. Semi-permanent implants are typically carried indwelling within the patient away from the healthcare facility and out from under the direct observation of a professional caregiver. They most usually remain indwelling during the patient's daily living for a period of days, possibly weeks, and possibly in some cases even years. These implants are generally intended to be carried within the patient for a limited period of time, however, and then to be removed.
Moreover, the terms “long-term” where herein used to describe an implantable device, or related system or procedure, include both permanent and semi-permanent implants unless otherwise specifically indicated or would be otherwise readily apparent to one of ordinary skill. Moreover, the use of the terms “permanent implant” generally contemplate similar application with respect to “semi-permanent implants” unless otherwise specifically indicated or readily apparent to be exclusive to one of ordinary skill.
Various medical device systems and methods have been disclosed related to chronic treatment of various medical disorders by delivering energy to tissue from permanent or semi-permanent implants. Many such prior disclosures relate specifically to providing implantable electrical energy delivery devices, and in particular relation to spinal cord stimulation. Many of such devices are intended to be long-term implants.
One example of a disclosed method of using a spinal cord stimulation lead involves implanting the lead in the epidural space and includes an elongate lead paddle located at the distal end of the lead. An array of electrodes is located on the lead paddle. The array has at least three columns of electrodes and includes a column having at least one electrode positioned substantially over the midline of the lead paddle, a column of at least one electrode positioned laterally of the midline on one side thereof, and a column of at least one electrode positioned laterally of the midline on the other side thereof. At least one of the columns within the array has more than one electrode. Each of the electrodes is interconnected by a conductor to a respective terminal at the proximal end of the lead. The lead is implanted such that the midline of the lead paddle is positioned over the midline of the spinal cord. Each electrode is independently selectable such that the spinal cord may be stimulated unilaterally or bilaterally.
Another example of an apparatus for multi-channel transverse epidural spinal cord stimulation uses a multi-channel pulse generator driving a plurality of electrodes mounted near the distal end of a lead. These electrodes are mounted in one or more lines, generally perpendicular to a lead axis, and having a planar surface along one surface of the lead. The lead is implanted adjacent to the spinal cord dura mater with the electrodes transverse and facing the spinal cord. Pulses generated by the pulse generator for each channel are normally simultaneous, of equal amplitude and of equal duration, however the pulse generator is arranged such that pulses for each channel can selectably alternate in time, can selectably be of unequal amplitude, or both. The changes in pulse timing and magnitude permit shifting the electrical stimulation field and the resulting paresthesia pattern after installation to accommodate improper lead placement or postoperative dislocation and to minimize unwanted motor responses.
A wide variety of spinal stimulation energy delivery systems and methods have been disclosed, generally with respect to providing electrical current to cause a nervous stimulation to produces a change in some innervated bodily function. For example, at least one disclosure involves an apparatus providing timed electrical stimulus pulses in the fluid of the sacral canal to conduct electrical stimulus to the spinal cord to stimulate miturition and certain muscles in paraplegic mammals, e.g. to evacuate the bladder.
In another example, a method for electrical spinal cord stimulation was disclosed for treating orgasmic dysfunction. Stimulating electrodes are placed in the spinal canal via a needle inserted between the appropriate vertebrae in parallel with the spinal cord. The electrodes are connected to a power source. Through variable transmission of electrical signals a patient suffering from orgasmic dysfunction may once again achieve orgasm.
Long-term, electrical spinal cord stimulation has been widely investigated for treating various types of pain, such as back pain in particular, as well as other types of pain such as angina.
According to at least one example, a facet joint pain relief method and apparatus is disclosed that depolarizes the medial branch of the spinal nerve associated with a painful facet joint so as to block pain impulses from reaching the spinal cord. The preferred apparatus includes a neurostimulator and two or more electrodes which carry electrical pulses to the target nerve or nerves. The impulses are intense enough to cause depolarization of a given medial branch and its articular branches, but not so large as to cause depolarization of the spinal cord itself. The stimulator in one regard is physically small and battery operated, facilitating implantation underneath the skin. The stimulator includes a controller and appropriate electronics operative to generate electrical impulses tailored to an individual's need for appropriate pain relief in terms of pulse frequency, pulse width, and pulse amplitude. In an alternative embodiment, the stimulator further includes electrodes and electrical circuitry operative to monitor myoelectrical activity generated by the surrounding muscles and modulate the impulses generated by the stimulator to meet the demands of the individual's activity and/or prolong battery life.
Another example provides a method and apparatus for providing feedback to spinal cord stimulation for angina treatment. Techniques for cardiac monitoring and angina pectoris treatment using a cardiac condition detector and stimulating electrode are disclosed. The detector and electrode are implanted, and angina is relieved by transmitting electrical pulses to the stimulating electrode while the patient is giving an indication of an ischemic event that otherwise would be indicated by the angina.
A variety of mechanisms have been previously disclosed that are intended to provide paths to and into bony structures of the spine for delivering a spinal implant there. Many disclosures have intended to address maintaining position of electrodes during electrical coupling to tissue. Several disclosures provide techniques intended for implanting a lead with therapy delivery elements, such as electrodes or drug delivery ports, within vertebral or cranial bone so as to maintain those elements in a fixed position relative to a desired treatment site. Additional techniques have been intended for non-invasively positioning and re-positioning the therapy delivery elements after implantation into such bone cavities. Further technique is disclosed using a position control mechanism and/or a position controller for adjusting in situ the position of the therapy delivery elements relative to the targeted tissue. The therapy delivery elements may be positioned laterally in any direction relative to the target, or toward or away from the treatment site. These techniques have been particularly intended for use with electrical stimulation or drug infusion to the targeted tissue.
Another disclosure provides an apparatus for providing a therapy in or through one or more trans-sacral axial instrumentation/fusion (TASIF) bore through vertebral bodies in general alignment with visualized, anterior or posterior axial instrumentation/fusion line (AAIFL or PAIFL) in a minimally invasive, low trauma manner and providing a therapy to the spine employing the trans-sacral axial bore. Anterior or posterior starting positions aligned with the AAIFL or PAIFL are accessed through respective anterior and posterior tracts. Curved or relatively straight anterior and curved posterior TASIF bores are formed from the anterior and posterior starting positions. The therapies performed through the TASIF bores include ductoscopy, full and partial discectomy, vertebroplasty, balloon-assisted vertebroplasty, drug delivery, electrical stimulation and various forms of spinal disc cavity augmentation, spinal disc replacement, fusion of spinal motion segments, and radioactive seeds implantation. Axial spinal implants and bone growth materials can also be placed in the TASIF bores.
Various disclosures have also been intended to provide feedback control for either adjusting the positioning of therapy delivery elements or other aspects of therapy, and in particular relation to spine therapy delivery elements.
In one group of examples, an apparatus and technique for electrical stimulation of the central or peripheral nervous system based upon changes in the position of a patient is disclosed. A position sensor is chronically implanted in the patient, such as in one specific example a mercury switch position sensor which indicates whether a patient is erect or supine. This position information is used by a chronically implanted pulse generator to vary the stimulation intensity. The intensity may be controlled by changes in pulse amplitude, pulse width, number of pulses per second, burst frequency, number of pulses per burst, electrode polarity, or other convenient parameter which accomplishes the particular medical purpose within an application. The output of the chronically implanted pulse generator is applied to the spinal cord, peripheral nerves, and/or targets in the brain with leads and electrodes in a manner consistent with the given medical need. Such stimulation is useful in the treatment of chronic intractable pain, hemodynamic insufficiency resulting in angina, peripheral vascular disease, cerebral vascular disease, various movement disorders, and bowel and bladder control.
Another example is directed toward living tissue stimulation and recording techniques with local control of active sites. Implantable electrodes are adapted to interact with electrically excitable tissue by an implantable, programmable controller that receives power from a main cable and data from a data conductor that identifies the stimulation and recording electrodes to be activated. The implantable controller enables electrical signals to be transmitted between a distal site of power generation and a selected subset of multiple electrodes with a minimum number of conductor wires.
Long-term electrical stimulus, such as via long-term implants, has also been investigated for promoting bone growth, in particular relation to the spine, as follows.
According to one general example, two electrodes are implanted into the tissue near the base site for bone growth. The electrodes are coupled to a bone growth stimulator which generates an alternating current that stimulates bone growth. Other examples using electrical stimulus to promote bone growth abound, in particular with respect to bony structures and implants related to the spine.
In one additional example, an implantable growth tissue stimulator and method is disclosed with a hand-held programmer/monitor for programming and monitoring an implantable tissue growth stimulator. The stimulator includes circuitry for implementing selected operations in response to a down-link signal transmitted by the programmer/monitor, various circuits such as control circuit and transmit/receive circuit is used for transmitting up-link and down-link signals to and from the implantable bone growth stimulator.
According to another example a preformed extendable mesh cathode for an implantable bone growth stimulator has been disclosed. An electrical signal generator is provided connected with an anode and a prefabricated wire mesh cathode that is extendable to at least twice its preformed initial length. The cathode in a preferred embodiment includes a single chain of conductive wire links formed as alternating loops and twists of two strands of monofilament titanium wire.
Still another example apparatus has been disclosed for the delivery of electric current for interbody spinal arthrodesis. Electrical current is delivered to an implant surgically implanted within the intervertebral space between two adjacent vertebrae of the spine to promote bone growth and the fusion process to areas adjacent to the implant. The implant is self-contained with a surgically implantable, renewable power supply and related control circuitry for delivering electrical current directly to the implant and thus directly to the area in which the promotion of bone growth is desired. The desired areas of bone growth promotion are intended to be controlled by conducting negative charge only to the desired location of promotion.
A further disclosed example provides direct current stimulation of spinal interbody fixation device has also been disclosed. A spinal fusion stimulator has an interbody fusion cage or other interbody fixation device adapted to be implanted in the intervertebral disc space of a patient's spine, the interbody fusion cage having a hollow body with internal and external conductive surfaces. The stimulator includes a constant current generator connected to the interbody fusion cage and set to provide a DC current effective to produce a surface current density of at least 1 uA/cm2 in the interbody fusion cage when implanted.
Additional long-term electrical delivery implant devices and related methods have been disclosed for other intended uses related for example to neural stimulation, nerve regeneration, and muscle stimulation.
At least one published example provides for nerve regeneration by way of electrical stimulus as follows. In vivo mammalian nerve regeneration of a damaged nerve is attempted by using an electric current through the damaged nerve while the nerve ends are abutted against one another, sutured together or spaced apart from each other. The apparatus is intended to be implantable in a human body so that the electric current can be maintained for an extended period of time to produce regeneration of the damaged nerve.
Various disclosures have also intended to provide percutaneous intramuscular stimulation electrodes, such as for treating shoulder dysfunction in patients who have suffered disruption of the central nervous system such as a stroke, traumatic brain injury, spinal cord injury, or cerebral palsey. An external microprocessor based multi-channel stimulation pulse train generator is used for generating select electrical stimulation pulse train signals. In another example, a closed-loop, implanted-sensor (e.g. force sensor), functional electrical stimulation system for partial restoration of motor functions is provided.
Further more detailed examples of devices, systems, and methods similar to those described above, such as with respect to long-term energy delivery implants, spinal therapy implants, or related devices and methods providing additionally helpful understanding, are variously disclosed in one or more of the following issued U.S. Pat. Nos. 4,569,351 to Tang; 4,750,499 to Hoffer; 4,774,967 to Zanakis et al.; 5,031,618 to Mullett; 5,282,468 to Klepinski; 5,342,409 to Mullett; 5,417,719 to Hull et al.; 5,441,527 to Erickson et al.; 5,501,703 to Holsheimer et al.; 5,565,005 to Erickson et al.; 5,643,330 to Holsheimer et al.; 5,766,231 to Erickson et al.; 5,824,021 to Rise; 6,014,588 to Fitz; 6,038,480 to Hrdlicka et al.; 6,112,122 to Schwardt et al.; 6,120,502 to Michelson; 6,169,924 to Meloy et al.; 6,171,239 to Humphrey; 6,270,498 to Michelson; 6,292,699 to Simon et al.; 6,319,241 to King et al.; and 6,436,098 to Michelson. Additional devices, systems, and methods are disclosed in the following U.S. Patent Application Publications: US 2001/0053885 to Gielen et al., now U.S. Pat. No. 6,795,737; 2002/0111661; 2003/0014088 to Fang et al. now U.S. Pat. No. 6,485,271. Additional examples are also disclosed in the following PCT Patent Application Publications: WO 99/56818 to Racz; and WO 00/78389 to Fitz. Another device is shown in the following U.S. Design Pat. Des. 361,555 to Erickson et al. The disclosures of these references listed variously throughout this paragraph are herein incorporated in their entirety by reference thereto.
Notwithstanding substantial benefits gained by many of the long-term implantable devices and chronic therapy methods previously described, each generally has respective limitations and shortcomings concomitant with their specified indications for use and with respect to certain therapies to which they are not generally applicable.
For example, the various disclosed not generally adapted to provide thermal therapy the many electrical therapy devices described are specially adapted to provide electrical nervous stimulus, and. Even to the extent thermal therapy may or would be delivered, however, such electrical devices and methods have shortcomings in their ability to deliver adequate thermal therapy to tissue as required, in particular in and around the spine, and in particular in a manner that penetrates structures sufficient to provide relatively deep heating from the energy delivery element, and/or that is controlled, directed, or focused for highly localized thermal treatment. Moreover, the various previously disclosed references do not adequately accommodate the need to control and isolate temperatures if thermal therapy were to be delivered, which is highly advantageous in particular during thermal treatment of structures in and around the spinal cord.
Still further, none of the previous disclosures noted above provide adequate devices and/or methods for controlling long-term thermal therapy of various tissues associated with skeletal joints, again in particular the spine, in order to achieve isolated, desired results such as thermal remodeling of tissue support structures (in particular stressed structures such as collagenous tissues of intervertebral discs), controlled cellular necrosis (including either in combination with or exclusive of tissue remodeling), or cellular regeneration or stimulation, or enhanced drug delivery.
At least two ultrasound systems and methods have been disclosed that are intended to provide ultrasound energy delivery to tissue via long-term implantable devices in order to treat chronic medical conditions such as of the types generally introduced above with primary respect to electrical energy delivery.
For example, ultrasonic techniques have been disclosed for using ultrasonic imaging to assist in neurostimulator control wherein the primary therapeutic energy delivery is electrical. A lead adapted to be implanted adjacent to a spinal cord located within a spinal column of a vertebrate in order to facilitate stimulation of the spinal cord or adjacent tissue. An ultrasonic transmitter/receiver produces an ultrasonic sound wave that creates ultrasonic echo waves reflected from a predetermined portion of the spinal cord and generates a distance signal related to the distance between the transducer/receiver and the predetermined portion of the spinal cord. The distance signal is used to adjust the amplitude of an electrical stimulation signal that stimulates the spinal cord or adjacent tissue so that the value of the stimulation signal tends to remain uniform in spite of changes in the relative distance between the transducer/receiver and the predetermined portion of the spinal cord. Accordingly, such use of ultrasound is as a diagnostic tool, and generally not therapeutic US energy delivery.
In another example, an apparatus and method that stimulates with ultrasound the growth of a tissue or produces an image at a site within a patient is disclosed. A housing may be subcutaneously implanted within the patient such that the ultrasound is directed toward the site. A generator disposed within the housing produces a signal, which a transducer converts into ultrasound. The transducer is partially disposed within the housing. The device may include an imaging circuit for processing ultrasound echoes received by the transducer to generate images of the tissue at the site. A remote control may be used to control the device while it is implanted within the patient.
Further more detailed examples of ultrasound devices and methods related to neurostimulator control and/or stimulating tissue growth are disclosed in the following issued U.S. Pat. Nos. 5,524,624 to Tepper et al.; and 5,628,317 to Starkebaum et al. The disclosures of these references are herein incorporated in their entirety by reference thereto.
Despite the benefits that such implantable ultrasound devices provide, they are still limited as to the ability to provide a wide variety of important long-term ultrasound therapies via permanent or semi-permanent implantable transducers. Moreover, other desirable features that are not provided by various of the prior electrical stimulation systems and methods are also not provided by these ultrasound devices and methods.
There is still a need for a long-term thermal or ultrasound therapy implant system that is adapted to provide one or more of the following beneficial features affecting the desired therapy: active and localized cooling of targeted and/or non-targeted tissues, use of ultrasonically transmissive coupling members to enhance energy delivery at the tissue interface, directionality, focusing and/or collimation of the US energy delivery, substantial depth of heating, and temperature and dosing controls around values adapted to provide various intended tissue responses (in particular within stressed tissues such as in spinal joints).
Moreover, the devices and related noted above lack the ability to provide additional benefits that may be harnessed from controlled, long-term ultrasound energy delivery into certain tissues in order to achieve a variety of desired tissue responses.
There is still a need for an improved, long-term implantable thermal therapy system that can be activated when necessary over prolonged periods of time in order to provide long term therapy to patients' joints, such as in particular spinal joints, in addition to other tissues in the body.
There is in particular still a need for a long-term, implantable ultrasound therapy system adapted to provide long-term ultrasound delivery to treat chronic ailments not adequately treated or cured by acute thermal therapy treatments.
There is also still a need for providing long-term thermal therapy to tissue, and in particular stressed tissue such as found in spinal joints, that allows for sufficient thermal doses to be delivered to achieve certain intended results according to lower elevated temperatures and over longer periods of time than otherwise currently available.
There is also still a need for a long-term implantable thermal therapy system and method that is adapted to provide long term, directional energy delivery into tissue within the body, in particular tissue associated with joints, and further more particularly spinal joints.
There is still a need for a system and method for locally delivering therapeutic amounts of ultrasound energy from long term implants within the body in order to treat disorders associated with the spine and other joints or tissues.
There is also still a need for a system and method adapted to locally deliver ultrasound energy to a highly localized region of tissue, such as only a portion of a disc associated with a spinal joint, when needed over long periods of time and without requiring multiple, repeat surgeries.